Green star polyps are an excellent beginner soft coral and might be the ideal first coral choice because they are:
- extremely hardy
- easy to care for
- tolerant of a range of water conditions
- don’t need a lot of light to grow
Let’s dive a bit deeper into what it takes to care for green star polyps in your home aquarium.
Table of contents
This article was re-written and updated in October 2020
Quick care guide facts
- Scientific Name: Pachyclavularia violacea
- Common Names: Green star polyps or GSP
- Care Level: Beginner/easy
- Aggression Level: Peaceful, but it will try to grow over everything in reach
- Color: Green polyps, white center, purple mat or stolon
- Coral Group: Soft corals
- Growth Form: Encrusting
- Key Nutrients: Nothing special to report here
- Temperature: 78-82 degrees Fahrenheit (25.5-27.8 C). Mine did survive a several day power failure, the temperature in the 50s (F)
- pH: 8.2
- Alkalinity: 8-12
- Calcium: 400 ppm
- Salinity(measured as specific gravity): 1.025
- Ammonia, nitrates, and nitrites = 0
Standard aquarium water parameters are perfect for these corals. Keep your water temperature stable, at around 78 degrees F. Use a high-quality reef salt mix, like Instant Ocean, and maintain a specific gravity around 1.025. Top off the tank with moderate-to-strong LED lights and at least low-to-moderate water flow, and after a few months, you’ll have to trim your green star polyps back to keep them from growing over everything.
It is worth mentioning that the ideal conditions listed above are ideal for most soft coral species. No special care is particularly required to keep these corals beyond the typical husbandry skills required for caring for any coral species.
GSP coral placement in a saltwater aquarium
GSP corals are not fussy and will likely thrive wherever you put them, as long as you have met the minimum conditions required: adequate light, water flow, and water quality.
However, the best placement for green star polyps in a reef tank is in an area with moderate flow and lighting. As shown in one of the images above, the colony in my tank spreads out along the back wall and side wall aquarium glass, but it tends to expand and retract over time, but the area most directly in the flow and under the lights tends to thrive all the time.
I’m convinced that the main reason for this cyclical growth pattern is related to the total amount of light. If I increased the light around the periphery of my tank, the growth could undoubtedly continue to even greater amounts.
GSP corals are partially photosynthetic and get nutrition from their symbiotic zooxanthellae. They also presumably absorb nutrients from the water column, as well, and have historically done well in systems with well-fed fish. Their polyps will also capture and pull in food particles that they catch in the water column. While target-feeding will likely increase growth rates, this coral grows quite well under normal reef aquarium conditions without supplemental feeding.
If you are new to the hobby, or if your green star polyp colony is one of the first in a new tank, you may want to consider target feeding to accelerate the growth and help fill in some empty substrates with living corals. But please keep in mind, this is already a naturally fast-growing coral, which may colonize more surface area than you had already planned.
Do you feed green star polyps?
Yes, you should feed your GSP. All corals are animals. This can sometimes be forgotten since we focus so much on having the right amount of light, but it is generally best to feed your corals.
Taxonomy, morphology, and body structure
The scientific name for Green Star Polyps (GSP) is Pachyclavularia violacea. Other names are starburst polyp, star polyps, and daisy polyps. According to Borneman, in Aquarium Corals, green star polyps were one time thought to be Clavularia viridis, but this is not correct. They are octocorallians–which means they belong to the class (subclass) of corals that have 8 tentacles on every polyp.
They are also part of the Alcyonacea order, which means they are part of the same part of the coral family tree as the leather corals. Each tentacle has a serrated appearance to it when examined close-up, as seen in the next image below.
Sorry that the image quality is so grainy. I took these photos in my own tank, without any special magnification gear. Literally just using the physical and digital zoom. Which also provides some context to the relative size of the serrations.
At the colony base, each of the polyps is attached to each other by a thick, rubbery purple matt, called a stolon.
You may hear the term “bulletproof coral” to describe some of the hardiest corals available in the hobby. It is certainly a curious phrase–and, of course, is an exaggeration.
Lighting requirements are fairly straightforward for this hardy, beginner soft coral.
- Avoid extremes (high and low intensity) in the lighting
- Acclimate the coral to your tank if you do have powerful LED aquarium lights
- Do not move the coral around a lot to different parts of your tank (changing light and water flow).
The polyps appear most aesthetically pleasing with some blue or actinic lighting to help make the green polyps pop, but they do not require this to grow in your tank.
Troubleshooting: Green star polyps closed or not opening in the tank
When disturbed, the polyps can fully retract into the stolon for protection.
This tends to happen:
- in response to cutting, fragging, or trimming back the coral
- at night time
- when stressed (like during power failures)
- when salinity is off (like when I haven’t topped off with fresh water in TOO LONG)
I’ve observed that the GSP polyps exhibit a shared response depending on the severity of the disruption. Minor disturbances tend to only cause a few polyps local to the disturbance to retract, but if I scrape away stolon and polyps covering up the slits in the overflow (a more dramatic disturbance), polyps across the entire colony will retract.
The coral looks like this, with its polyps retracted:
These are one of the easiest corals to frag since they are an encrusting species that will grow on just about any substrate. If you line up a few pieces of live rock rubble touching the rock the green star polyps (GSP) are on, the polyps will grow out from the base rock and encrust the rubble.
Free up the frags by cutting the purple mat, called a stolon, with a knife or scissors.
If you want to learn how to frag green star polyps or any other coral, download my definitive guide.
Compatibility in a tank with GSP (Pachyclavularia violacea)
Unlike some other coral species, green star polyps do not have stinging tentacles, called nematocysts, so they are relatively peaceful and compatible with other coral species. GSP grows quickly and encrust on anything within reach–including your other corals.
So if you want to keep green star polyps with other coral species, you need to maintain physical separation between the rocks the GSP are growing on and neighboring rocks, or the green star polyps will eventually take over all the connected rocks.
Green star polyps are a fantastic beginner coral because they grow fast and adapt well to life inside a home aquarium. Because they will grow on just about any substrate, they are a great coral to get creative within your tank. GSPs will grow up the aquarium glass or overflow. They can encrust wires or tubes, so if you can, turn any surface inside your aquarium into a fuzzy, living mat. My green star polyps have grown up the back wall of the tank in my display tank (technically an overflow). Where can you grow them?
GSP will grow on any aquarium surface, including the aquarium glass, plastic, live rock, and even other corals. I have witnessed all three behaviors directly in my own tanks. The image below was taken in my display tank a few years ago. Notice how the coral is growing up the back wall (that’s where the overflow is) and is growing out on the sidewall.
Each year in my tank, the GSP coral seems to go through a series of growth and recession cycles. My tank is a 92-gallon bowfront aquarium. There is a central, massive GSP coral colony covering most of the back wall of the aquarium and the live rock in the back — and the coral grows outward, on the side glass in both directions. The polyps attempt to grow forward over every surface, including rocks, other corals, and aquarium glass.
Check out this short video all about green star polyps
Are green star polyps poisonous?
GSP is not poisonous in the same way that zoanthid polyps are poisonous. Some palythoa zoanthid species have a toxic chemical called Palytoxin that they release when stressed. Learn more about palytoxin (not associated with green star polyps) here.
Hopefully, this goes without saying, but your GSP is not for human consumption, regardless of what I just wrote regarding palytoxin. Finally, just because they don’t have palytoxin doesn’t mean they won’t damage neighboring corals as they grow. They will. Hope that helps.
Natural range for Pachyclavularia violacea.
GSP is native to the rubble areas of reefs and lagoons and is often found with Xenia and Clavularia, commonly in areas that are typically nutrient-rich with low water flow (Borneman 2001).
Where to find this soft coral for sale
GSP corals are an aquarium staple and are available at most local and online stores. Considering how well they grow and can be fragged, I’m always a bit surprised by the price tag at some stores. Especially since anyone growing this soft coral would likely give away a frag for just a few dollars. But I know operating a local fish store is a tough business. I suspect these popular corals help keep the lights on.
What to read next
Green star polyps are a popular coral species for reef tank owners. Check out out a few of these other great coral species:
To learn more about caring for green star polyps in your reef tank, watch this video here:
Written by Albert B. Ulrich III–author of The Reef Aquarium Series of books: The New Saltwater Aquarium Guide, How to Frag Corals, 107 Tips for the Marine Reef Aquarium, and Reef Journal.